A device that is known in the art to be used for measuring intraocular pressure on an open eye comprises a probe, one part of which is made of a magnetic material and the other part, of nonmagnetic material having a rounded (hemispherical) base for deforming the eye, the probe being placed within an electromagnetic winding to impart a desired speed to it, the electromagnetic winding being built into the wall of the housing held in the operator's hand during measurement (see: Patent WO 03/105680 [PCT/F103/00489], A61B3/16, published on Dec. 24, 2003).
The prior art device for measuring IOP uses the force of impact to deform an open eye, but no static load is applied. IOP measurement through the eyelid does not give the desired accuracy because IOP measurement through the eyelid requires significantly larger energy than is used on an open eye to compensate for the shock-absorbing properties of the eyelids that have a different anatomical structure. Increasing the impact force, however, leads to instability of the spatial position of the eye because of the stretching of the muscles to which the eye is attached. Instability does not allows IOP to be measured with desired accuracy. Moreover, the rounding at the probe base is objectionable when IOP is measured through the eyelid with a large impact load as it causes excessive pain during measurement.
Also known in the art are devices for measuring IOP through the eyelid while the eye position is stabilized, for example, by applying further static load to the eye.
For example, a prior art device for measuring intraocular pressure comprises an annular support through which a static load is applied to the eye during measurement and a ball weighing 0.3 to 0.7 gram to deform the cornea of the eye through the eyelid by impact force, the ball being dropped in a free fall from a height of 120 to 150 mm, followed by measuring the pressure according to the height of the first rebound of the ball (see: Russian Patent 2,007,951, class A61B3/16, published in 1994).
The use of an annular support prevents the IOP measuring device from being attached firmly to the eye, so its accuracy is reduced significantly. Besides, a further measurement error increases sharply with the device deflected even insignificantly from the vertical during measurement.
The closest prior art of this invention is a device comprising a housing containing a bushing capable of moving therein within a limited range and provided with guides and a supporting part to apply a constant desired load; an eyeball deforming element in the form of a free-falling body provided within the interior of the bushing and capable of dropping in a free fall under the effect of its own weight to apply an impact load; a deformation element holder in the initial top position thereof in the top part of the movable bushing; a measuring winding built into the wall of the movable bushing and connected to the generator circuit to measure the movement function of the deformation element over time; a sensor to indicate the position of the movable bushing relative to the housing in the form of a mechanical catch registering the initial bottommost position of said bushing within the housing, including a spring-biased button, the clamping part of which is placed in an aperture of the housing wall for engaging the outer surface of the movable bushing, the supporting part of the movable bushing being provided with two projections having round support ends equally spaced at a distance of 7 to 10 mm from the movement axis of the free-falling body; the elastic deformation element being shaped as a rod having a flat base 1 to 7 mm2 in area; and the bottom guide serving to limit the lower position of the deformation element within the movable bushing in an inoperative state (see: Russian Patent No. 2,123,798, class A61B3/16, published in 1998).
In the prior art device, an impact force is developed during measurement by a free-falling rod having a flat base 1 to 7 mm2 in area, and a static load is applied to the eye through the eyelid by a movable bushing having a measuring winding built therein together with means to register the initial position of a rod impacting the eye through a support of an original design allowing the device to be firmly attached to the eye through the eyelid.
The prior art device, though, requires to be held in an absolutely vertical position during measurement and furthermore it requires the rod to be set in its initial position before measurement and several measurements to be taken to enhance accuracy, so that the measurement process lengthens, and the patient himself is unable to measure his IOP.
The low accuracy of IOP measurement by the prior art device is caused by the effect of the device housing being placed manually in a vertical position; the absence of means to automatically check the accuracy with which the device is positioned during measurement; and the error produced by the mechanical clamp developing the desired static load during measurement.
The invention is aimed at improving the operating characteristics of a device for IOP measurement through the eyelid.